The present invention relates to a process for the suspension smelting of sulfidic and mixed ord or concentrates in order to separate the impurity minerals or metals present in them.
The process according to the invention thus relates to improving the refinability of sulfidic complex and mixed ores or concentrates. These ores and concentrates usually contain copper, nickel, cobalt, and iron as their principal components. Owing to the manner in which the ores were formed they also contain, in addition to the principal components, elements which are to be considered impurities in regard to them, either quantitatively or qualitatively, but are often rare and therefore valuable. The impurities are heavy and often easily vaporizable elements, usually with a high number in the periodic system, such as Zn, Cd, Hg, Ga, In, Tl, Ge, Sn, Pb, As, Sb, Bi, Mo, W, Re. The said elements usually form very stable polymorphous complex compounds with arsenic, antimony and bismuth plus the principal metal, or between themselves.
Some of these elements--e.g., As, Sb, Bi, Pb, Zn, Sn--cause very great problems in the metallurgy of copper and nickel. In conventional pyrometallurgical refining processes these components, being easily dissociated into metals from their compounds, accompany the principal metal through the various stages of the process. Although some of these components are removed from the system at each stage of the refining process, some of them remain in the crude metal and even in very low concentrations entirely prevent or greatly complicate its further refining.
The invention thus relates to a process for removing the impurity minerals or metals present in sulfidic complex and mixed ores and concentrates by the suspension smelting technique. According to the process, some of the elements which are present in complex ores and greatly disturb their metallurgical treatment can be removed entirely or to a considerable degree from the sulfide matte and slag phases created as molten products.
The metals covered by the process which are to be considered impurities in regard to the principal metals (copper and/or nickel) but are often very rare and therefore valuable include the heavy elements usually with a high number in the periodic system, such as (group-period-metal): II-4,5,6-Zn, Cd, Hg; III-4,5,6-Ga, In, Tl; IV-4,5,6-Ge, Sn, Pb; V-4,5,6As, Sb, Bi; VI-5-Mo; VII-6-Re.
Several of these components form highly complex mineral structures with the principal metals or between themselves. For the implementation of the process under discussion it is advantageous, especially if the concentrations of the impurity metals are high, to rearrange the complex minerals into simple or independent sulfide minerals before processing.
To illustrate the present-day technological level of the suspension and suspension vaporization processes, the development of suspension processes is discussed here generally and some examples are given of the numerous suspension vaporization processes. The known processes comparable with that according to the invention are mainly vertical suspension processes in which either conventional reaction shaft smelting or cyclone smelting is used.
The first large-scale technological application of vertical suspension smelting is the process according to U.S. Pat. No. 2,506,557, developed mainly for the refining of sulfidic copper concentrates. The application of the same process to pyrite concentrates for the production of elemental sulfur is described in U.S. Pat. No. 3,306,708 and, in a more developed form, in Canadian Pat. No. 844,504. The reduction of the sulfur dioxide present in the smelting plant gases by means of solid carbon by the suspension process has been solved in the process according to Canadian Pat. No. 867,269. The reduction of the slag phase with a valuable metal content obtained in the production of rich copper matte, the sulfidization of the flying dusts, and the reduction of the smelting plant gases to the desired quantity in vertical suspension smelting are the essence of the process according to Canadian Pat. No. 909,517. The suspension smelting of iron-poor nickel sulfide matte by zone reduction for the selective sulfidization of nickel and for the system for lowering the ferric iron is performed by the process according to U.S. Pat. No. 3,754,891. Finally, in the development of vertical suspension smelting we should mention the processing of very finely-divided oxidic and sulfidic ores and concentrates according to Finnish Pat. No. 48,202 and the manufacture of crude copper and converter matte by the process according to Finnish Patent Application 1992/74.
In connection with the said vertical suspension smelting processes, impurity components pass both mechanically and chemically into the gas and flying dust phases. Owing to the methods, equipment technology, and other factors, the quantities which are transferred are, however, very low when using conventional processes.
The use of vertical suspension smelting for vaporizing impurities or the principal metal is undoubtedly best known in the processes developed by Prof. Alfred Lange. In Lange's process (e.g., GDR Pat. 18, 783 and GFR Pat. 1,052,692) concentrates, flying dusts, industrial intermediate products, etc. with high zinc and lead concentrations are strongly oxidized in suspension at a high temperature (1000.degree.-1600.degree. C.) in the upper part of a vertical reaction shaft. The upper part of the reaction shaft, having a considerably greater diameter than the lower part, comprises a cyclone-resembling part which is either spherical or elongated into a cylinder with spherical ends; the concentrate-air suspension in a strong turbulent motion produced by tangential blowing in the concentrate disperser is fed into this part. Additional air and fuel are fed tangentially into the cylindrical or spherical part. Thereby the vaporizable components of the concentrate are caused to pass into the gas phase, and the non-vaporizable sulfidic and other components, under the effect of centrifugal forces, impinge against the cylinder walls, from where they flow through the narrower shaft part into the matte and slag collecting tank in the lower furnace. Under the reaction shaft, secondary air is fed into the furnace in order to burn the still unburned compounds in the shaft product and the fuel, and the heat amount thereby obtained is used for covering the heats of reaction and thermal losses in the lower furnace. According to the process, the increased delay period necessary for the vaporization and the control of the settling period of the molten and solid materials are obtained by means of the turbulences in the upper part of the reaction shaft and by means of additional air and other gases. The secondary air can be used not only for the above control but also for controlling the concentration in the copper matte in the collection tank.
The lower-furnace floor in Lange's furnace system rises from the horizontal level (towards the rising shaft). Before the rising shaft or under it there can be, sunk in the furnace floor, a "pocket" for the recovery of mechanical dusts. This dust chamber can also be located after the rising shaft. The construction of the furnace system has a decisive role in the process. These furnace constructions have been described not only in the patent but also in, for example, the following publications: A. Lange: Metallurgie u. Giessereitechnik, 4, H12, 1954, 538-547; A. Lange, J. Barthel: Bergakademie 9, 1961, 554-563.
The concentrates and byproducts of the Lange vaporization process, as well as the vaporizable compounds and metals (e.g., Zn, Pb, Sn, Cd, Ge, Re), are mentioned, in addition to the said publications, in, for example: J. Barthel: Freib. Forsch H, B 112, 1965, 13-36; Leipner: Neue Hutte, 16, H 7, 1971, 395-399.
What is most noteworthy is the very high impurity contents in the matte and slag phases obtained in Lange's vaporization process. The following analysis values (Me, % by weight) are given as an example (GDR Pat. 18 783):
Feed 1./2. 41.8/22.0 Zn; 0.96/16.0 Pb; 0.5/0.5 Cu PA0 Matte 1./2. 5.9/7.6 Zn; 0.10/9.5 Pb; 56.6/7.2 Cu PA0 Slag 1./2. 6.77/3.24 Zn; 0.06/0.20 Pb; -/0.12 Cu PA0 Dust 1./2. 60.8/47.9 Zn; 2.7/18.7 Pb; -
Another example of the separation of lead and zinc from molten products by the vertical suspension process is the process according to Rumanian Pat. 54 991. The process includes the conventional vertical suspension smelting process and a feed burning apparatus. It should be noted that the process actually comprises nothing novel in comparison with the known vertical suspension processes. The described concentrate burner hardly produces any strong effect on the vaporization, either. It should be mentioned that the concentrate burner (description and figure on p. 5) mentioned in the specification is by its structure almost analogous to Lange's vertical burner (cf. A. Lange: Advances in Extractive Metallurgy, Elsevier 1968, 206-223, FIG. 4, p. 211). The examples in the patent specification do not give the necessary data concerning the total feed and the total air, the thermal losses determining the additional gas amount, etc. so that the vaporization results given as examples in the specification cannot be evaluated by using known laws of nature. Nevertheless, according the patent, when the operation rate (i.e., the feed capacity of the furnace unit) is increased when manufacturing by the process a matte with a 30-40% copper concentration (concentrate 6-12 Pb, 17-30 Zn, 5-7 Cu), concentrations of 8-9 Zn, 0.8-1.2 Pb, 1-1.5 Cu in the slag can be expected, and the slag is treated in an electric furnace. The impurity concentrations in the matte are not given in the specification.
Cyclone smelting and processes developed from it constitute a very important group among the impurity vaporization processes. In the vaporization processes the apparatus technology is often crucial for the implementation and development of the process. The effective suspension vaporization and burning at the very high temperature in the cyclone and the flexible possibilities for varying the location and position of the cyclone are of decisive importance in vaporizing processes. The cyclone burner can be located in connection with the smelting furnace in such a manner that the combustion and vaporization gases can be directed out of the system without the gases coming into contact with the products of smelting. A description of the construction and placement of the cyclones (horizontal or vertical--gases withdrawn from the bottom or from the top--two-step cyclones, etc.) is given in, for example: I.M. Rafalovich, V.L. Russo: Tsvetnye Metally, 9, 1964, 30-39. The vaporization of impurity components (Re, Mo, Se, Te, Cd, Pb, Zn, Ge) in cyclone smelting when smelting copper and polymetallic concentrates is described in I.A. Onajew: Neue Hutte, 10, H 4, 1965, 210-216.
As to the cyclone vaporization of concentrates, the processes according to U.S. Pat. No. 3,555,164 and GFR Pat. 2 038 227 are discussed.
In the former process, the molten and solid material emerging from the vertical cyclone impinges against a dam wall below the cyclone, from where it flows into a matte-slag separation tank which is connected at one end to an electric furnace through a partition (communicating vessels). In the electric furnace the slag is purified and the vaporizing metals (Zn, Pb, etc.) are condensed from the gas phase. The gases emerging from the cyclone and the impurity components present in them (Pb, Zn, Cd, Se, Re, Hg, etc.) flow out of the system in a direction opposite to that of the molten and solid flow, directly into the dust and gas treatment devices.
The process according to the latter patent is an embodiment of the former. According to this process the concentrate is burned in the cyclone until it is completely devoid of sulfur. For example, the flying dust which contains part of the impurities is separated from the obtained gas phase and returned to the cyclone along with the feed. The molten and solid materials not containing sulfides pass, analogously to the previous process, from the dam wall into the electric furnace separated from the gas space by a partition. In the electric furnace the vaporizable components are separated from the oxide mass by reduction and recovered. Thus, in the process the bulk of the impurities is transferred to the oxide phase and not recovered until the electric furnace. The flying dust phase which is refed into the smelting system need thus not be treated separately.
An interesting application of the cyclone furnace is described in British Pat. No. 1,001,310. In the process, zinc is vaporized from the granulated slag of the lead shaft furnace by feeding it into a vertical reaction shaft by means of a cyclone. The carbon dust used as fuel and the air preheated by means of the furnace outlet gases (500.degree.-550.degree. C.) are fed by means of two tangential burners fitted at different levels in the reaction shaft.
Also worth mentioning is the roasting of pyrites and chalcopyrites, and the purification of the calcines, comprising many different vertical suspension processes. The aim is to remove sulfur, arsenic, antimony, and valuable metals from the calcines. The processes are usually one- or two-stage oxidation and reduction processes nearly always connected with a sulfating, chlorinating or vaporizing roasting. The processes are usually performed in fluidized-bed furnaces. Some examples of the latest technology are the processes according to U.S. Pat. No. 3,649,245 and Canadian Patent Nos. 890,343, 876,030, 885,378, and 882,585.